/
capture_helper.rb
187 lines (182 loc) · 6.66 KB
/
capture_helper.rb
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require 'active_support/core_ext/object/blank'
module ActionView
module Helpers
# CaptureHelper exposes methods to let you extract generated markup which
# can be used in other parts of a template or layout file.
# It provides a method to capture blocks into variables through capture and
# a way to capture a block of markup for use in a layout through content_for.
module CaptureHelper
# The capture method allows you to extract part of a template into a
# variable. You can then use this variable anywhere in your templates or layout.
#
# ==== Examples
# The capture method can be used in ERb templates...
#
# <% @greeting = capture do %>
# Welcome to my shiny new web page! The date and time is
# <%= Time.now %>
# <% end %>
#
# ...and Builder (RXML) templates.
#
# @timestamp = capture do
# "The current timestamp is #{Time.now}."
# end
#
# You can then use that variable anywhere else. For example:
#
# <html>
# <head><title><%= @greeting %></title></head>
# <body>
# <b><%= @greeting %></b>
# </body></html>
#
def capture(*args)
value = nil
buffer = with_output_buffer { value = yield(*args) }
if string = buffer.presence || value and string.is_a?(String)
NonConcattingString.new(string)
end
end
# Calling content_for stores a block of markup in an identifier for later use.
# You can make subsequent calls to the stored content in other templates, helper modules
# or the layout by passing the identifier as an argument to <tt>content_for</tt>.
#
# Note: <tt>yield</tt> can still be used to retrieve the stored content, but calling
# <tt>yield</tt> doesn't work in helper modules, while <tt>content_for</tt> does.
#
# ==== Examples
#
# <% content_for :not_authorized do %>
# alert('You are not authorized to do that!')
# <% end %>
#
# You can then use <tt>content_for :not_authorized</tt> anywhere in your templates.
#
# <%= content_for :not_authorized if current_user.nil? %>
#
# This is equivalent to:
#
# <%= yield :not_authorized if current_user.nil? %>
#
# <tt>content_for</tt>, however, can also be used in helper modules.
#
# module StorageHelper
# def stored_content
# content_for(:storage) || "Your storage is empty"
# end
# end
#
# This helper works just like normal helpers.
#
# <%= stored_content %>
#
# You can use the <tt>yield</tt> syntax alongside an existing call to <tt>yield</tt> in a layout. For example:
#
# <%# This is the layout %>
# <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
# <head>
# <title>My Website</title>
# <%= yield :script %>
# </head>
# <body>
# <%= yield %>
# </body>
# </html>
#
# And now, we'll create a view that has a <tt>content_for</tt> call that
# creates the <tt>script</tt> identifier.
#
# <%# This is our view %>
# Please login!
#
# <% content_for :script do %>
# <script type="text/javascript">alert('You are not authorized to view this page!')</script>
# <% end %>
#
# Then, in another view, you could to do something like this:
#
# <%= link_to 'Logout', :action => 'logout', :remote => true %>
#
# <% content_for :script do %>
# <%= javascript_include_tag :defaults %>
# <% end %>
#
# That will place <script> tags for Prototype, Scriptaculous, and application.js (if it exists)
# on the page; this technique is useful if you'll only be using these scripts in a few views.
#
# Note that content_for concatenates the blocks it is given for a particular
# identifier in order. For example:
#
# <% content_for :navigation do %>
# <li><%= link_to 'Home', :action => 'index' %></li>
# <% end %>
#
# <%# Add some other content, or use a different template: %>
#
# <% content_for :navigation do %>
# <li><%= link_to 'Login', :action => 'login' %></li>
# <% end %>
#
# Then, in another template or layout, this code would render both links in order:
#
# <ul><%= content_for :navigation %></ul>
#
# Lastly, simple content can be passed as a parameter:
#
# <% content_for :script, javascript_include_tag(:defaults) %>
#
# WARNING: content_for is ignored in caches. So you shouldn't use it
# for elements that will be fragment cached.
def content_for(name, content = nil, &block)
content = capture(&block) if block_given?
@_content_for[name] << content if content
@_content_for[name] unless content
end
# content_for? simply checks whether any content has been captured yet using content_for
# Useful to render parts of your layout differently based on what is in your views.
#
# ==== Examples
#
# Perhaps you will use different css in you layout if no content_for :right_column
#
# <%# This is the layout %>
# <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
# <head>
# <title>My Website</title>
# <%= yield :script %>
# </head>
# <body class="<%= content_for?(:right_col) ? 'one-column' : 'two-column' %>">
# <%= yield %>
# <%= yield :right_col %>
# </body>
# </html>
def content_for?(name)
@_content_for[name].present?
end
# Use an alternate output buffer for the duration of the block.
# Defaults to a new empty string.
def with_output_buffer(buf = nil) #:nodoc:
unless buf
buf = ActionView::OutputBuffer.new
buf.force_encoding(output_buffer.encoding) if output_buffer && buf.respond_to?(:force_encoding)
end
self.output_buffer, old_buffer = buf, output_buffer
yield
output_buffer
ensure
self.output_buffer = old_buffer
end
# Add the output buffer to the response body and start a new one.
def flush_output_buffer #:nodoc:
if output_buffer && !output_buffer.empty?
response.body_parts << output_buffer
new = ''
new.force_encoding(output_buffer.encoding) if new.respond_to?(:force_encoding)
self.output_buffer = new
nil
end
end
end
end
end